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遇到要求一个运算表达式的计算结果的问题
传进的是一个字符串 (字串内容当然是表达式了)
最终要求出运算结果

之前在 JScript 或 VBScript 里通常是 eval 来解决
下面给个 Java 的

只能算 +-*/ 还有括号

/**
 * (#)Calculator.java　　　　创建时间：Apr 30, 2009 6:14:03 PM 
 */
package cn.ialvin.util;

import java.util.Stack;
import java.util.regex.Pattern;

/**
 * @author 林志斌(ialvin.cn) 广东 普宁 里湖
 */
public class Calculator {
 
 public static void main(String[] args) {
 String exp = "-3.3 + 1.5 * (- 3 + -5)";
 Calculator calculator = new Calculator();
 System.out.println(calculator.cal(exp));
 }
 
 public double cal(String exp) {
 exp = adj(exp);
 exp = conver(exp);
 Stack<Object> stack = new Stack<Object>();
 String[] cs = exp.split("[^\\d.+\\-*/]+");
 int i = 0;
 while (i < cs.length) {
 String c = cs; i++;
 if ("+".equals(c)) {
 stack.push((Double)stack.pop() + (Double)stack.pop());
 } else if ("-".equals(c)) {
 stack.push(0 - (Double)stack.pop() + (Double)stack.pop());
 } else if ("*".equals(c)) {
 stack.push((Double)stack.pop() * (Double)stack.pop());
 } else if ("/".equals(c)) {
 stack.push(1 / (Double)stack.pop() * (Double)stack.pop());
 } else {
 stack.push(Double.parseDouble(c));
 }
 }
 return Double.parseDouble(stack.pop().toString());
 }

private String adj(String exp) {
 exp = exp.replaceAll("[^\\d.+\\-*\\/()]+", "");
 exp = exp.replaceAll("(^|[(+\\-*\\/])\\-([\\d.]+)", "$1(0-$2)");
 return exp.replaceAll("[+\\-*\\/()]", " $0 ").trim();
 }
 
 private String conver(String exp) {
 String[] str = exp.split("\\s+");
 Stack<String> expStack = new Stack<String>();
 for(int i = str.length - 1 ; i >= 0 ; i--)
 expStack.push(str);
 Stack<String> outStack = new Stack<String>();
 Stack<String> operStack = new Stack<String>();
 operStack.push("#");
 while (expStack.size()> 0) {
 String c = expStack.pop().toString();
 if (c.matches("^\\d+(?:\\.\\d*)?$")) {
 outStack.push(c);
 } else if ("(".equals(c)) {
 operStack.push(c);
 } else if (")".equals(c)) {
 if (operStack.lastElement().equals("(")) {
 operStack.pop();
 } else {
 expStack.push(c);
 outStack.push(operStack.pop());
 }
 } else {
 if (comparison(c, operStack.lastElement()))
 outStack.push(operStack.pop());
 operStack.push(c);
 }
 }
 operStack.remove(operStack.firstElement());
 while(!operStack.empty())
 outStack.push(operStack.pop());
 return outStack.toString().replaceAll("\\[|\\]|\\,", "");
 }
 
 private int getLevel(Object o) {
 if ("(".equals(o)) return 1;
 if ("+".equals(o)) return 2;
 if ("-".equals(o)) return 2;
 if ("*".equals(o)) return 3;
 if ("/".equals(o)) return 3;
 return -1;
 }
 
 private boolean comparison(String c1 ,Object c2) {
 return getLevel(c2)-getLevel(c1) >= 0;
 }
}

posted on 2009-05-03 22:29 林俊海閱讀(540) 評論(0) 編輯收藏

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